1. Field of the Invention
This disclosure relates to the field of medical devices, specifically to the use and structure of balloon angioplasty or dilatation catheters.
Despite being in widespread use for over 20 years and substantial development efforts, the delivery of angioplasty balloons to a target lesion in a patient's vasculature is often a challenge. During delivery, the operator often has to overcome tortuous anatomy, long and calcified lesions (especially in peripheral arteries) and tight turns. Further difficulties can arise from the need to cross previously treated lesions where restenosis has occurred.
Balloon catheters are usually delivered over a guide wire that is inserted into the vasculature and through the target lesion prior to advancement of the balloon catheter. With most balloon catheters, the operator controls advancement by pushing/pulling the catheter shaft from over the guide wire. During delivery, the operator will push the catheter shaft over the guide wire until the balloon reaches the target lesion. When encountering an obstacle, the operator can pull back and push again forcefully in the hope that the balloon catheter will overcome this obstacle. Some catheters have improved torque transmitting capabilities but these are limited and work best in short balloons.
In conventional balloon catheter constructions, at least at a distal segment of the shaft near the balloon is made from a relatively soft polymer material which is very ineffective for transmitting pushing force and torque to the catheter tip, typically relying on the stiffness of the guide wire which is often insufficient. The balloon region of a balloon catheter is made of a very thin folded balloon; it is the weakest in terms of push force and torque. The distal section of the balloon is attached to the catheter's guide wire lumen at the very distal end of the catheter, and to the catheter distal shaft (but only to the inflation lumen and not to its internal concentric guide wire lumen) on its proximal balloon taper. Therefore this segment of the catheter has inefficient structural integrity in delivering the push force to the catheter tip in attempt to overcome an obstacle.
The difficulties described above are exacerbated in catheters having long balloons, such as those used in peripheral arteries. Such balloons can reach or exceed 30 cm in length. Further difficulty arises in peripheral arteries when attempting to cross the iliac arch where wire bending may occur as the push force is not effectively transferred to the distal part of the catheter. Attempts to reinforce the catheters using metallic inner members or stiff members have failed since the catheter must be flexible in order to travel through the arteries without damaging the vessels. Other limitations to reinforcing the balloon include the need to keep a low profile (minimize the addition of new materials or layers of tubing) and the need to have short inflation/deflation times (maximizing the area of the inflation lumen to allow rapid liquid flow into the balloon during inflation and out of the balloon during deflation).
Thus, the ability of balloon catheters and especially balloon catheters with long balloons used to treat peripheral arteries (with balloon lengths up to 30 cm) to reach and cross target lesions is often limited and can prolong procedures requiring the use of excessive contrast media and radiation, both of which can be harmful to the patient.
For all of the above reasons, it would be desirable to provide improved angioplasty balloon catheters and methods for their use. In particular, it would be desirable if the balloon catheters could have improved pushability or column strength, particularly over their distal regions comprising the balloon, as well as improved torqueability, and thus be capable of being advanced through tortuous regions of the vasculature and through restricted, difficult-to-pass vascular lesions. In addition to possessing such improved column strength and torsional stiffness, it is desirable that the flexibility of the distal region of the catheter, particularly that comprising a balloon, remain sufficiently high to that the balloon remains sufficiently conformable to be delivered around tight bends and through tortuous regions of the vasculature. At least some of these objectives will be met by the inventions described below.
2. Description of the Background Art
Patents describing balloon angioplasty catheter constructions include U.S. Pat. Nos. 7,491,213; 7,635,347; 7,273,470; 7,022,106; 6,030,405; and 5,827,231.